Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

255
FXUS63 KLOT 130555
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1255 AM CDT Mon Apr 13 2026

.KEY MESSAGES...

- Summer-like temperatures will continue Monday through
  Wednesday with highs in the upper 70s to lower 80s and
  overnight lows in the 60s.

- Waves of severe thunderstorms (all hazards including flash
  flooding) may occur in the region as early today but more
  likely Tuesday and Wednesday.

- A brief break in the pattern is expected on Thursday before
  another storm system arrives in the Friday to Saturday
  timeframe.

- A transition toward a cooler and less stormy pattern is
  favored by early next week.

&&

.UPDATE...
Issued at 810 PM CDT Sun Apr 12 2026

Monitoring two items for this evening and overnight:

The first is the potential for a combination of gradient and
precip-induced strong wind gusts later this evening as an area
of showers--currently developing across the St. Louis metro--
pivot northward into the region. During this time (roughly 10
PM to 1 AM), this activity will intersect a nocturnally-
intensifying low-level jet, with 925 mb wind speeds progged to
increase to around 55 knots. Recent guidance such as the RAP,
HRRR, and HRDPS have somewhat consistently shown an increase in
in near-surface lapse rates and attendant surface gusts,
particularly south of I-80 and east of about I-55. It`s always
difficult to determine exactly how the near-surface stable layer
will respond in these situations, but it certainly won`t take
much to transport 50+ mph gusts to the ground given the already
weak static stability in place. Have increased wind gusts a bit
to account for this potential. If observations indicate a marked
increase in gusts later this evening, could end up needing a
short-fused wind advisory for parts of the area.

The second item revolves around the potential for a secondary
axis of shower and thunderstorm development south of I-80
overnight. This activity would be focused on the nose of an
eastward-advancing pool of increased 925-850 mb moisture and on
the tail end of a departing 700 mb shortwave and right at the
leading edge of the main incoming EML plume. While this signal
is not ubiquitous across the guidance suite, there is enough of
one to justify adding some low end chances for thunderstorms
during the overnight period.

Carlaw

&&

.DISCUSSION...
Issued at 1252 PM CDT Sun Apr 12 2026

This Afternoon through Tonight:

A recent hand surface analysis places a 996 mb low pressure
system near the North Dakota, South Dakota, and Minnesota
borders early this afternoon. A warm front extends eastward away
from the center of the low across northern Wisconsin and
central Lower Michigan, while a hybrid cold front/dry line
extends southward through the southern Plains. Much of the
Mississippi River Valley, including our local area, is in the
broad warm sector of the deepening cyclone. Aside from
southwesterly winds gusting 30 to 40 mph, it is otherwise a
beautiful mid-April afternoon with partly cloudy skies and
temperatures in the mid 70s to lower 80s.

With continued broad southwesterly flow across the Mississippi
River Valley, an upper-level shortwave currently lifting into
central Missouri will progress northeastward and into the Lower
Great Lakes this evening. Gradually increasing DCVA atop a
somewhat moist and largely uncapped mixed layer should support
the development of scattered showers as soon as 3 PM primarily
northwest of I-55 this afternoon. Coverage of showers should
increase steadily thereafter and peak across our area between 6
PM and 10 PM as the heart of the wave passes directly overhead.
With the instability profile remaining fairly low-centric (a
consequence of meager lapse rates near 6 K/km), the threat for
lightning with showers this afternoon and evening remains low
(15% or lower). While this evening does not look like a complete
washout, keep a rain jacket handy if out and about!

Monday and Monday Night:

Over the next 48 hours, aggregate troughing will become
established across the southwestern United States and reinforce
longwave ridging from the Mississippi River Valley toward the
East Coast. Northeasterly shortwave shedding will support
corresponding episodic surface cyclone development from the
Plains through the Upper Great Lakes, altogether reinforcing a
broad warm sector with summer-like temperatures into the middle
Mississippi River Valley through midweek. Indeed, highs Monday
through Wednesday are favored to remain in the upper 70s to
lower 80s while overnight lows will only "fall" into the low to
mid 60s.

As the aforementioned aggregate troughing strengthens across
the southwestern US tonight into Monday, a renewed push of
southwesterly mid-level flow will advect a plume of steep mid-
level lapse rates (>8 K/km) into the Great Lakes. The
combination of stout capping at the base of the EML plume,
neutral to modestly positive mid-level height tendencies, and a
lack of robust mechanisms to force ascent collectively suggest
that daylight hours on Monday will remain dry. However, locally
augmented convergence along the edges of advecting EML plumes
usually supports agitated ACCAS that, if clumped enough to
locally cool/moisten the base of the outer edge of the cap, can
lead to surprise convection. Accordingly, will manually pencil
in a northeastward-moving ribbon of 20% PoPs for thunderstorms
tomorrow during the afternoon and evening hours keeping in mind
the heavily favored (80% chance) outcome is a completely dry
day. Should a thunderstorm develop, effective shear of 30 to
35kt, weak effective inflow, and steep mid-level lapse rates
would support a threat for supercells with both damaging winds
and hail. Again, we heavily favor tomorrow being dry across our
area.

Tomorrow night, intense supercellular (and potential GWAC)
development is favored to occur somewhere from central Minnesota
into central Wisconsin as a subtle upper-level shortwave riding
within broad upper-level southwesterly flow excites a low-level
jet atop the stalled warm frontal zone. With the northeasterly
terminus of the low-level jet pointing toward the west-to-east
oriented instability axis from Wisconsin and eventually central
Lower Michigan, any upscale growth into a mesoscale convection
system should stay decidedly north of our area. However, should
the warm front end up further south than currently in our
forecast (as hinted by HRDPS/ECMWF output), part of northern
Illinois may get a glancing blow by storms toward daybreak
Tuesday. Currently don`t see this as a particularly likely
scenario, so will cap PoPs at 30% favoring areas north of I-88
through the overnight hours.


Tuesday into Wednesday:

Toward the middle of the week, aggregate troughing will shift
eastward toward the Four Corners Region leading to a
corresponding "nudge" eastward in broad upper-level
southwesterly flow into the Great Lakes. The overlap of the
plume of steep mid-level lapse rates, stalled frontal zone, a
steady feed of low-level moisture advection, and a parade of
shortwaves and the eventual ejection of the aggregate trough
with associated jet maxima to support deep-layer shear will
support a threat for additional waves of severe thunderstorms in
the general region. Storm modes ranging from convective
clusters to supercells with a threat for all hazards (including
tornadoes) will be fair game. And, repeated rounds of storms
over the same area will support a threat for flash flooding
(locally significant). With all of that said, pinpointing
favored locations and time windows will remain challenging until
there is better clarity on exact shortwaves and eventual
placements of boundaries. This is all to say, the Tuesday
through Wednesday timeframe continues to look quite busy in our
neck of the woods.


Thursday onward:

Ensemble model guidance advertises only a brief break in the
summer-like and stormy pattern on Thursday as shortwave ridging
moves through the Great Lakes ahead of a substantial trough
digging into the central US. High temperatures look to rebound
into the low to even mid 80s by Friday accompanied by another
threat for strong to severe thunderstorms Friday night into
Saturday. Thereafter, there is a reasonably strong signal in
ensemble guidance for a cooldown to start next week.

Borchardt

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1255 AM CDT Mon Apr 13 2026

Key aviation forecast messages:

- MVFR CIGs (IFR at RFD) expected overnight through the AM with
  IFR possible at times.

- A conditional threat for severe TSRA exists this afternoon.
  Confidence in storms forming remains low (30% chance).

- LLWS concerns return late evening through early Tuesday AM.

The back edge of the gusty showers will be exiting the area
within the next hour. A small cluster of showers and isolated
thunderstorms may develop yet early this morning and move across
areas mainly south of I-80 between ~7-11Z. Can`t fully rule out
the northern periphery of this activity approaching MDW/GYY and
will monitor radar trends closely.

MVFR stratus will remain in place through the night and
potentially through much of the morning hours today at the
Chicago area terminals. IFR ceilings will prevail at RFD and may
occur at times overnight at ORD/DPA. Also can`t rule out a
period of MVFR VSBYs in BR outside of Chicago prior to daybreak.

A conditional threat of severe thunderstorms exists this
afternoon into early evening. While substantial capping is
expected across the area, if elevated thunderstorms can initiate
as some of the hi-res guidance are indicating, damaging winds
and hail would be possible in addition to heavy downpours.
Given the lower confidence in storms forming, have elected to
introduce only a PROB30 for TSRA for now in a broader window
from 19-00Z (1 hr earlier at RFD and 1 hr later at GYY).

Winds will remain at least sporadically gusty through the night
out of the southwest with gusts in the 20-25 kt range then ease
slightly after daybreak remaining SW to SSW through the day. The
low-level jet ramps up again late this evening through early
Tuesday morning. Even with gusty surface winds at least marginal
low-level wind shear concerns may develop given 50-55 kt as low
as 2000 ft.

We will also be keeping an eye on any potential upstream
convective elements that may try to dip into northeast Illinois
toward daybreak Tuesday, though confidence remains too low to
include any mention in the TAFs with this update.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 AM CDT early this morning for the
     IL and IN nearshore waters.

&&

$$

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